A broad array of sweet compounds including monosaccharide and disaccharide sugars (glucose, fructose, sucrose), sugar alcohols, small molecule non-caloric sweeteners (saccharin, cyclamate, sucralose), dipeptides (aspartame, neotame), and protein sweeteners (monellin, thaumatin, brazzein) exist for use as food additives and to sweeten products from toothpaste to pharmaceutical preparations. However, it has been clear that humans have a preference for the naturally occurring sweeteners over the artificial non-caloric sweeteners that have been developed over the years.
Prior to the molecular identification of the primary sweet taste sensor as a heterodimeric combination of two family C G protein coupled receptors (GPCRs), T1r2+T1r3 (reviewed in Bachmanov A A, Beauchamp, 2007), it had been proposed that sweet taste might rely on sugar transporters or sugar-gated cation channels (DeSimone J A, Heck G L, Mierson S, Desimone S K., 1984; Mierson S, DeSimone S K, Heck G L, DeSimone J A., 1988; Simon S A, Labarca P, Robb R., 1989; Simon S A, 1991). Glucose transporters (GLUT), sodium glucose co-transporters (SGLT) and KATP metabolic sensors play important roles in glucose homeostasis and metabolism throughout the body and in many specific organs (e.g. gut, pancreas, heart, skeletal muscle, brain) (reviewed in Scheepers A, Joost H G, Schürmann A., 2004; McTaggart J S, Clark R H, Ashcroft F M., 2010; Nichols C G., 2006; Zhao and Keating, 2007). However, the presence and function in taste cells of these important proteins are largely unknown. Liu et al. (Acta Histochemica, 2010) identified SUR1 (a component of KATP) in rat fungiform taste cells, but found SUR1 to be absent from rat circumvallate taste cells. Liu et al did not examine taste cell type specific expression. Hevezi et al. (PLoS One, 2009) identified GLUT8, GLUT9, GLUT10, GLUT13, SLC2A4RG (a regulator of GLUT4) and the insulin receptor as genes potentially expressed in macaque taste cells/buds. However, these authors did not confirm the expression of these genes in taste cells or determine if they are expressed in specific types of taste cells.